This invention relates to a rotary actuator, and more particularly relates to a rotary actuator adapted to be utilized in, for example, a hydraulic damping device of the adjustable damping force type.
As one example of a hydraulic damping device of the adjustable damping force type, there is disclosed in "The Weekly Service No. 489" issued by Nissan Motor Co., Ltd. in September 1983 a hydraulic damping device in which damping force can be adjusted by rotating an adjusting rod inserted through a bore formed in a piston rod of the damper.
U.S. patent application Ser. No. 824,965 filed on Jan. 31, 1986, now U.S. Pat. No. 4,686,863 and assigned to the same entity as this application discloses a rotary actuator which is designed to rotate an adjusting rod in a piston rod of a hydraulic damper which constitutes a hydraulic damping device as described above. The rotary actuator comprises a motor, a transmission mechanism coupled to the motor, a first rotor connected to the transmission mechanism and adapted to be rotatable around a first axis, and a second rotor adapted to be rotatable around a second axis which is eccentric with respect to the first axis and is connected to an adjusting rod in a piston rod of a hydraulic damper. In order to change the damping force mode, the motor is switched on to rotate the first rotor through the transmission mechanism. Then, a projection formed on an upper surface of the first rotor engages with a projection formed on a lower surface of the second rotor to rotate the second rotor through a predetermined angle.
However, the rotary actuator mentioned above is not provided with means for holding the second rotor stationary after the second rotor has been rotated through the predetermined angle. Therefore, when, for example, the second rotor is rotated in the direction opposite to the normal one in installing the actuator in a vehicle, it is possible that the projection of the first rotor will be strongly pressed against the projection of the second rotor such as to bite into the same. Further, since the actuator is mounted on a vehicle, the second rotor may unintentionally rotate by virtue of vibration of the vehicle. Therefore, when the amount of the unintentional rotation is relatively large, the hydraulic damping device may be operated accidentally. In these circumstances there has been a need for an actuator which is more reliable in operation.
The present invention has been accomplished in view of the aforesaid circumstances and the object of the invention is to provide a rotary actuator which is reliable in operation and which makes it possible to reliably change the damping force mode of a hydraulic damper.